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Chlamydospermous seeds document the diversity andabundance of extinct gnetalean relatives in Early Cretaceous vegetation
Swedish Museum of Natural History, Department of Paleobiology.ORCID iD: 0000-0001-7587-9687
Oak Spring Gardens.ORCID iD: 0000-0003-4331-6948
Aarhus University.ORCID iD: 0000-0003-3038-0967
2019 (English)In: International journal of plant sciences, ISSN 1058-5893, E-ISSN 1537-5315, Vol. 180, p. 643-666Article in journal (Refereed) Published
Abstract [en]

Premise of research. The recognition of diverse and abundant chlamydospermous seeds from the Early Cretaceous of Denmark, Portugal, and eastern North America has been an unexpected outcome of studies of mesofloras that were initially focused on early angiosperms. These seeds provide structural information critical for understanding morphological and structural diversity in an important Mesozoic group of extinct gnetalean relatives.

Methodology. The fossil seeds were picked from Early Cretaceous mesofossil floras from localities in western Portugal and Virginia using a stereomicroscope. Selected seeds were studied in more detail for morphological and anatomical traits using SEM and synchrotron radiation X-ray tomographic microscopy.

Pivotal results. Six new species of chlamydospermous seeds are described that add substantially to the known diversity of Early Cretaceous chlamydosperms. In general seed organization, the fossils are similar to seeds of extant Gnetales, but none of the fossils can be assigned to any of the three living genera of Gnetales (Ephedra, Gnetum, and Welwitschia). All six species have similar closure of the micropylar canal but show considerable variation in the anatomy of the seed envelope. In micropylar closure, the fossils are most similar to extant Gnetum, but they differ in other respects from seeds of extant Gnetum, and one of the new seed taxa has polyplicate, ephedroid pollen in the micropyle. A well-preserved embryo with two cotyledons is preserved in seeds of Rothwellia foveata and provides the first information on the embryo in this Early Cretaceous chlamydospermous complex.

Conclusions. The chlamydospermous seeds described here show similarities to seeds of extant Gnetales. However, most of the fossils exhibit combinations of features that are unknown among extant species of Gnetales and clearly represent an extinct complex of plants that were important in Early Cretaceous vegetation, along with other extinct plant groups, including Bennettitales and Erdtmanithecales.

Place, publisher, year, edition, pages
Chicago: University of Chicago Press, 2019. Vol. 180, p. 643-666
Keywords [en]
BEG group, Bennettitales, chlamydospermous organization, Ephedra, ephedroid, Erdtmanithecales
National Category
Natural Sciences
Research subject
Ecosystems and species history
Identifiers
URN: urn:nbn:se:nrm:diva-3404DOI: 10.1086/704356OAI: oai:DiVA.org:nrm-3404DiVA, id: diva2:1372240
Funder
Swedish Research Council, 2014-5228Available from: 2019-11-22 Created: 2019-11-22 Last updated: 2019-11-25Bibliographically approved

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Friis, Else MarieCrane, Peter RobertPedersen, Kaj Raunsgaard
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